The present invention relates to a motor drive control device that includes a power supply converter that is connected to an alternating-current power supply, an inverter that is connected to a motor, and an energy storage device that is connected to a direct-current bus that connects the power supply converter and the inverter.
A motor drive control device that includes a power supply converter connected to an alternating-current power supply and an inverter connected to a motor has been widely known and used as a device that drives a motor (i.e., power source) used for many industrial machines. An industrial machine is not necessarily operated so that the load or the rotational speed is constant (i.e., the load or the rotational speed may vary to a large extent). Moreover, one process (or one processing cycle) may include one or more constant load periods or load change periods.
Therefore, a device in which an energy storage device is provided in a direct-current circuit between the power supply converter and the inverter to reduce a change in power supplied from the alternating-current power supply with respect to a change in power required for the motor has been proposed (JP-A-2000-236679). A device that allows a change in direct-current voltage due to a change in load during acceleration or deceleration of the motor by causing the power supply converter to increase the direct-current voltage before acceleration and causing the power supply converter to decrease the direct-current voltage before deceleration, has also been proposed (JP-A-2005-204391).
According to these devices, since the storage state of the energy storage device and the power-running/regeneration state with respect to the alternating-current power supply can be adjusted by controlling the direct-current voltage, the alternating-current peak value and the size of the alternating-current power supply can be reduced.
The above devices are designed on the assumption that the power supply converter always operates. This aims at dealing with a situation in which the load and the rotational speed of the industrial machine and the operational state of the motor vary to a large extent, and improving adaptability and generality.
When the power supply converter always operates, the thermal rating of the power supply converter must be determined taking account of such an operational state. Therefore, the size of a cooling fin or the like must be increased. Moreover, a loss occurs due to such an operational state.
The motor drive control device is not sufficiently improved by merely providing the energy storage device to reduce the size of the alternating-current power supply and reduce cost. Specifically, it is important to reduce the size of the power supply converter in order to improve the entire motor drive control device (i.e., industrial machine).